Geographical Distributions

A. farnesiana originated in the northern part of tropical America, where its closest relatives can also be found. It is the most widely distributed Acacia species, introduced to all tropical and subtropical regions of the world for its fragrant flowers and has become widely naturalized and sometimes weedy, e.g. in the southern United States and Australia. In Malesia, the Spaniards first introduced it to the Philippines from Mexico. It is now recorded throughout South-East Asia. It was first cultivated in Europe in the Hortus Farnesianus in Italy in 1611 and has become an important crop in southern France.

Description

It is a branched shrub or rarely a small tree up to 4(-10) m tall. The bark is rough and light brown. The branchlets are cylindrical, greyish-brown to purplish-grey, hairless with prominent lenticels.

Leaves, lateral shoots and peduncles are arranged alternate, often arising from short spurs on older wood. The leaflet is arranged in pairs along each side of a common axis twice and compound. The whitish-grey stipules are sharp-pointed, straight, up to 5 cm long. The petiole is 0.5-1.3 cm long, with a circular, sessile and often raised gland present in the distal half. It has a 4-6 cm long rachis, sometimes with a gland near the apical leaflet of a pinnate leaf. The base is truncate while the apex is asymmetrically acute, ending abruptly in a short stiff point. Both surfaces are hairless with the main vein is not centred, lateral veins beneath are raised and prominent.

Inflorescence is composed of spherical stalk with a cluster of heads in a common ring of 50-60 flowers, aggregated in groups of 1-7 flowers in the upper leaf-axils. The stalk is 0.8-3.5 cm long, with a ring of bracts (involucel) at the summit and hidden by the flowers.The flowers are sessile, with 5 parts in a flower-whorl, golden-yellow and fragrant. The sepal is 1-1.3 mm in diametre, tube hairless with five 0.2 mm long teeth, triangular, acute, hairless except for the exterior of the apex. The petal is 2.3-2.5 mm long and the tube is hairless. The lobes come in 5, elliptical and about 0.5 mm long. It is acute, scarcely covered with short soft hairs at the apex. The stamens are numerous, 4-5.5 mm long with glandless anthers. The ovary is supported by a small 1.5 mm long stalk, densely covered with short soft hairs.

Seeds are ellipsoidal, 7-8 mm x 4-5.5 mm, in 2 rows, obliquely transverse in the pod, embedded in a sweet pulp. They are slightly flattened, olive-brown to olive-green also light brown to dark brown or black. The areole is elliptical, 6.5-7 mm x 4 mm, opens towards the scar on the seed that indicates its point of attachment.

Ecology / Cultivation

A. farnesiana is mostly found as a dominant component of secondary vegetation in dry places, but tolerates a wide range of annual rainfall (up to 4000 mm) and prefers a long dry season. Annual rainfall in its habitat in Australia ranges from 150-700 mm. It requires a mean annual temperature of 15-28°C and occurs from sea level up to 1500 m altitude. Its natural distribution in Malesia is up to 400 m altitude, while in cultivation it grows up to 1200 m. Frost is tolerated to a minimum of -5°C. It is found scattered or in pure, open stands in plains, savanna grasslands, tidal flats, sandy river beds, brushwood, and waste ground, on heavy soils including black clays, loamy or sandy soils with a pH of 5-8(-10). In France, however, A. farnesiana may grow and flower poorly on alkaline soils. It tolerates saline conditions and fire.